Leases (Supplemental Cash Flow and Other Information Related to Leases) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases	$ 127
Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from finance leases	6
Cash paid for amounts included in the measurement of lease liabilities: Financing cash flows from finance leases	7
Right-of-use assets obtained in exchange for new finance lease liabilities	2
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 86
Weighted-average remaining lease term: Operating leases	7 years
Weighted-average remaining lease term: Finance leases	19 years
Weighted-average discount rate: Operating leases	9.20%
Weighted-average discount rate: Finance leases	5.70%